Lake levels
Grand Lake St Marys, OH
- water level
- 870.70 ft
- Condition
- Falling
- 7-day change
- -0.16 ft
- 30-day change
- -0.04 ft
- 1-year change
- +1.47 ft
Reading as of 2026-10-12 | the U.S. Geological Survey
- Since yesterday
- -0.02 ft
- 7-day change
- -0.16 ft
- 30-day change
- -0.04 ft
- 1-year change
- +1.47 ft
- Record high
- 871.68 ft
In brief
Grand Lake St Marys stood at 870.70 feet on Oct 12, 2026.
Source: U.S. Geological Survey
Lake level timeline
Records and averages
| Current level | 870.70 ft |
|---|---|
| Record high | 871.68 ft (2026-09-18) |
| Record low | 868.59 ft (2025-12-29) |
| Average of all readings | 869.79 ft |
| Data span | 3 years (1,149 readings) |
Level schematic
Frequently asked questions
Is Grand Lake St Marys full right now?
As of 2026-10-12, Grand Lake St Marys sits at 870.70 ft. Over the past 30 days the level has fallen 0.04 ft.
What is the water level at Grand Lake St Marys today?
The most recent reading at Grand Lake St Marys is 870.70 ft (2026-10-12), sourced from the U.S. Geological Survey. Readings on this page refresh automatically as the agency publishes new data.
What is the highest Grand Lake St Marys has ever been?
The highest level for Grand Lake St Marys in our records is 871.68 ft on 2026-09-18. The lowest is 868.59 ft on 2025-12-29. Our record covers about 3 years of readings.
Why is Grand Lake St Marys low right now?
Reservoir levels move for four main reasons: rainfall and runoff into the basin, releases through the dam for downstream water supply, power generation or flood control, evaporation during hot months, and seasonal drawdown schedules set by the operating agency. Grand Lake St Marys has fallen 0.04 ft over the past 30 days. For the operational reason on any given week, check the U.S. Geological Survey directly.
How much has Grand Lake St Marys changed over the past year?
Grand Lake St Marys is +1.47 ft compared with this date last year (870.70 ft today). The full-history chart above covers 3 years, with a record high of 871.68 ft and a record low of 868.59 ft.
Download and cite
Quote this reading
Grand Lake St Marys stood at 870.70 feet on Oct 12, 2026.
Download the full record
grand-lake-st-marys-oh-water-level-history.csv
How to cite
MyWaterLevel, “Grand Lake St Marys water level, 2023 to 2026,” data from U.S. Geological Survey, https://mywaterlevel.com/lake/oh/grand-lake-st-marys/, accessed Oct 13, 2026.
Source: the U.S. Geological Survey. All Ohio lake levels. Readings are provisional and may be revised. About our data and methods.